Predictive value of latent tuberculosis tests in Indian healthcare workers: a cohort study

To the Editors: Healthcare workers (HCWs) in high tuberculosis (TB)-burden countries are known to have a substantially higher risk of latent TB infection (LTBI) and TB disease [1], and this has been demonstrated repeatedly in India [2, 3]. Several studies have evaluated interferon-γ release assays (IGRAs) in HCWs [4], but no study has reported the predictive value of IGRAs in this population of HCWs at risk for TB exposure. Between January and June 2004, we had performed a cross-sectional comparison of the tuberculin skin test (TST) (1 tuberculin unit of purified protein derivation RT23) and QuantiFERON®-TB Gold In-Tube (QFT; Cellestis Ltd, Melbourne, Australia) in a cohort of 726 HCWs (719 had valid test results for both tests) at the Mahatma Gandhi Institute of Medical Sciences (Sevagram, India), with young trainees making up half the cohort [5]. A total of 360 (50%) HCWs were found to be positive using either the TST or QFT assay at baseline, and 226 (31%) were found to be positive using both tests. The prevalence estimates of TST and QFT positivity were comparable, with high concordance between test results [5]. Although isoniazid preventive therapy (IPT) was offered to HCWs with positive baseline TST or QFT results, only a small proportion had completed INH therapy. In 2010, ∼6 yrs after …